Combined biochemical and immunocytochemical approaches are undertaken to study specific stimulus responses in parotid secretory cells. Cyclic nucleotide-mediated protein phosphorylation is investigated to determine specific intracellular sites/loci and mechanisms of regulatory action in the signal processing of salivary cells during protein secretion. Accordingly, cyclic-3', 5'-adenosine monophosphate (cyclic AMP)-dependent protein kinase activity and its intracellular compartmentalization is measured in rat parotid tissue stimulated in vitro by the norephinephrine analogue isoproterenol and compared to that of unstimulated controls. Endogenous phosphoproteins and specific protein substrates which are phosphorylatively modified after stimulation are identified by employing electrophoretic separation and autoradiographic techniques. Morphological tissue changes are followed using both light and electron microscopy. Secretory product and lysosomal enzyme localization and transport will be accessed by immunological and immunocytochemical methods employing antibodies produced either conventionally in rabbits or by monoclonal methods by murine hybridomas.